Image forming apparatus and method of controlling same

ABSTRACT

One scanning interval of a laser beam is divided into a plurality of blocks, correction data, which corresponds to optical characteristics of an optical unit placed between a laser element and a photosensitive drum, is stored in memory in association with each block, the correction data corresponding to a block being scanned by the laser beam is read out of the memory, and the laser is driven upon correcting the laser drive signal based upon the correction data read out and correction data corresponding to a block adjacent to the block being scanned by the laser.

FIELD OF THE INVENTION

This invention relates to an image forming apparatus for irradiating anelectrically charged photosensitive material with a laser beam andforming an electrostatic latent image to thereby form an image.

BACKGROUND OF THE INVENTION

An image forming apparatus for forming an image by electrophotographyincludes a charging unit for uniformly charging the photosensitivesurface of a photosensitive drum, a latent-image forming unit forforming an electrostatic latent image, which conforms to imageinformation, on the charged photosensitive surface, a developing unitfor developing the electrostatic latent image using toner, and atransfer unit for transferring the developed latent image to a printingsheet. The apparatus executes image forming processing successivelywhile rotating the photosensitive drum.

Among the types of photosensitive drums that can be used, an amorphoussilicon drum has a higher durability that than of an organicsemiconductor drum employed generally in the prior art and has alreadyfound practical use in monochrome copiers. However, a characteristic ofan amorphous photosensitive drum is that it exhibits sensitivityunevenness ascribable to a variance in the thickness of thephotosensitive film, this being a problem related to manufacture.Sensitivity unevenness affects charging and the exposure characteristicand gives rise to irregular density in the image formed. Further,density unevenness in an image is produced not only by sensitivityunevenness of the photosensitive drum but also by a variance in theoptical unit inside the image forming unit. The variance in the opticalunit referred to here is attributed to the mounting precision of lensesand mirrors within the optical unit. With an optical unit that has aplurality of lasers, the variance manifests itself as a deviation in theimages obtained by irradiation with the lasers and as a shift in theoptical axis.

Such density unevenness has not posed much of a problem in the past butis now a problem that the market cannot allow owing to the demand forhigher image quality in recent years.

In an effort to solve this problem, the conventional approach has beento suppress variance in the optical unit per se, i.e., to suppressvariance by raising the mounting precision of the lenses and mirrors inthe optical unit, or to select manufactured parts that satisfy certainconditions so that variance is held below a prescribed value, or toimprove the finished precision of the component parts. Alternatively, asdisclosed in the specification of Japanese Patent Application Laid-OpenNo. 7-294837, polarized-light correcting means is provided within theoptical unit and a correction is applied by the correcting means,thereby uniformalizing the amount of light in scanning so as to suppressdensity unevenness.

With these examples of the prior art, however, it is necessary tosuppress the sensitivity unevenness of the photosensitive drum or toraise the precision of the optical unit and to perform the requiredadjustments and selections. The result is in increase in the cost of theapparatus.

SUMMARY OF THE INVENTION

Accordingly, a feature of the present invention is to eliminate thedrawbacks of the prior art.

Another feature of the present invention is to provide an image formingapparatus and method of controlling same in which unevenness of aphotosensitive drum or optical unit is corrected to enable the formationof a high-quality image while a rise in the cost of the apparatus issuppressed.

According to an aspect of the present invention, there is provided withan image forming apparatus for irradiating an electrically chargedphotosensitive material with a laser beam and forming an electrostaticlatent image to thereby form an image, comprising:

storage means for dividing one scanning interval of the laser beam intoa plurality of blocks, and

storing correction data, which corresponds to optical characteristics ofan optical unit placed between a laser element and the photosensitivematerial, in association with each block;

readout means for reading first correction data, which corresponds to ablock being scanned by the laser beam, out of the storage means; and

driving control means for correcting a drive signal of the laser elementand driving the laser element based upon the first correction data,which has been read out by the readout means, and second correctiondata, which corresponds to a block adjacent the block being scanned bythe laser beam.

Further, according to another aspect of the present invention, there isprovided with a method of controlling an image forming apparatus forirradiating an electrically charged photosensitive material with a laserbeam and forming an electrostatic latent image to thereby form an image,comprising:

a step of storing correction data corresponding to electrificationcharacteristics of the photosensitive material;

a readout step of reading first correction data, which corresponds to ablock being scanned by the laser beam, out of the memory; and

a driving control step of correcting a drive signal of the laser elementand driving the laser element based upon the first correction data,which has been read out in the readout step, and second correction data,which corresponds to a block adjacent the block being scanned by thelaser beam.

The above-described features are attained by a combination of thefeatures set forth in the main claim. The dependent claims stipulateuseful specific examples of the invention.

The gist of the invention does list all the necessary features andtherefore subcombinations of groups of these features are also possibleaccording to the present invention.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 depicts a schematic structural view for describing the overallstructure of a color copier according to an embodiment of the presentinvention;

FIG. 2 is a block diagram for describing the structure of a laserirradiation unit and its peripheral units in a color printer accordingto this embodiment;

FIG. 3 depicts a diagram useful in describing the concept of acorrection by a correction unit in an optical unit according to a firstembodiment;

FIG. 4 is a block diagram illustrating the structure of the correctionunit according to the first embodiment;

FIG. 5 is a diagram useful in describing the placement of correctiondata that has been stored in a memory;

FIG. 6 is a timing chart for describing the generation of correctiondata by the correction unit according to the first embodiment;

FIG. 7 is a block diagram for describing a correction unit and a drivercircuit of a semiconductor laser according to a second embodiment of thepresent invention; and

FIG. 8 is a flowchart for describing laser drive control in a colorprinter according to this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings. It should be notedthat the embodiments set forth below do not limit the invention setforth in the claims. In addition, the combinations of features describedin the specification are not all necessarily essential for attaining theobjects of the invention. Furthermore, a color copier having a singlephotosensitive drum is described in the embodiments. However, thepresent invention is not limited to such a single-drum type copier. Forexample, the invention may include a plurality of image forming unitsfor the colors Y (yellow), M (magenta), C (cyan), Bk (black) arrangedalong the transport path of a printing sheet.

FIG. 1 depicts a schematic structural view for describing the overallstructure of a color copier according to an embodiment of the presentinvention.

This color copier is equipped with an image reader (hereinafter, a colorscanner) 1 for reading a color original and generating a color imagesignal corresponding to the color original, and a color image printingunit (hereinafter, color printer) 2.

The color scanner 1 forms the image of an original 3 on a color sensor 7via an illuminating lamp 4, mirror group 5 (5A to 5C) and lens 6, readscolor image information of the original 3 for each of the separatedcolors of blue (B), green (G) and red (R) and generates color signalsand converts each of these color signals to an electrical image signal.The image signals of each of the color components B, G, R generated bythe color scanner 1 are subjected to color conversion processing by animage processing unit (not shown) so that image data of the colorcomponents represented by colorants such as inks of black (Bk), cyan(C), magenta (M) and yellow (Y) are obtained from the three primarycolors (R, G, B) of light.

The color printer 2 will be described next.

Color image data of the components C, M, Y, Bk from the color scanner 1enters a laser irradiation unit (optical unit) 28, which converts theimage data to laser light to scan a photosensitive drum 21 upon beingreflected by a polygon mirror 57. The surface of the photosensitive drum21 is electrically charged uniformly by a charger 27, after which thesurface is exposed by laser light from the laser irradiation unit 28. Asa result, an electrostatic latent image conforming to the image of theoriginal is formed on the surface of the photosensitive drum 21. Thelatter is rotated in the counter-clockwise direction, as indicated byarrow A. Provided about the photosensitive drum 21 are a drum cleaningunit (which includes a device for removing electric charge prior tocleaning) 212, the charger 27 and a rotating developer 13 comprising anM developer 13M, a C developer 13C, a Y developer 13Y and a Bk developer13K held on a rotary body. The rotating developer 13 is rotated and isplaced at a position where the M developer 13M, C developer 13C, Ydeveloper 13Y and Bk developer 13K will contact the photosensitive drum21, whereby the toner of the corresponding color becomes affixed to thephotosensitive drum 21 in conformity with the electrostatic latent imageon the photosensitive drum 21. Whenever the electrostatic latent imageof each color is formed on the photosensitive drum 21, the color imageis transferred to an intermediate transfer belt 22, which is anintermediate transfer body. Thus, a full-color image that is the resultof superposition of images of the colors Y, M, C, Bk is formed on theintermediate transfer belt 22. The image transfer to the intermediatetransfer belt 22 is implemented by the action of a primary transfer viaroller 217. The intermediate transfer belt 22 is engaged by a driveroller 220 for transporting and driving the intermediate transfer belt22 by a drive motor, and a group of follower rollers 218, 219, 237. Asecondary transfer bias roller 221 is disposed at a position opposingthe follower roller 219 of the intermediate transfer belt 22, and amechanism for driving the secondary transfer bias roller 221 so as tobring it into and out of contact with the intermediate transfer belt 22.A belt cleaning unit 222 is provided at the surface of the intermediatetransfer belt 22 at a position opposing the follower roller 237. Theoperation timing at which the belt cleaning unit 222 makes and breakscontact with the belt 22 is such that the belt cleaning unit 222 isspaced away from the belt 22 from the start of printing until thetrailing end of the image of the final color is transferred from thebelt 22 to the printing sheet. Then, at a prescribed timing thereafter,the belt cleaning unit 222 is contacted with the belt by a mechanism(not shown) to clean the intermediate transfer belt 22.

Image transfer to the printing sheet will be described next. Theuppermost printing sheet of a plurality of printing sheets accommodatedin a paper cassette 223 is extracted from the paper cassette 223 byrotation of a pick-up roller 224 and is conveyed to the transferposition of the secondary transfer bias roller 221 through a pair ofconveyance rollers 226, 225. A full-color image on the intermediatetransfer belt 22 is transferred to the printing sheet by the contactpressure and bias potential of the secondary transfer bias roller 221.The printing sheet to which the color image has thus been transferred issent to a fixing unit 25, where the image is fixed.

It should be noted that each of the developers 13M, 13Y, 13C, 13Kcomprises a developing sleeve that rotates to bring the crest of thedeveloping agent (toner) into contact with the surface of thephotosensitive drum 21 in order to develop the electrostatic latentimage, and a developing paddle that rotates in order to draw up and stirthe toner in each developer.

FIG. 2 is a diagram useful in describing the structure of the laserirradiation unit 28 and its peripheral units in the color printer 2according to this embodiment. Components similar to those in FIG. 1described above are designated by like reference characters.

When a semiconductor laser 55 is driven by a laser driving controller 54based upon an image signal 202 generated by an image signal generator53, a laser beam 205 is emitted from the semiconductor laser 55. Afterpassing through a collimating lens 56, the laser beam 205 is reflectedby a polygon mirror 57 and converted to a scanning signal. The reflectedlaser beam passes through an fθ lens 58 and is reflected by a mirror 59to thereby scan the surface of the photosensitive drum 21 along thelongitudinal direction of the drum 21. As a result, the electrostaticlatent image corresponding to the image signal is formed on the surfaceof the photosensitive drum 21. A beam detector (BD) 60 detects the starttiming of one scan by the laser beam and generates a horizontalsynchronization signal. An input unit 61 inputs correction data, whichis described later, to a correction unit 52.

The operation of the laser irradiation unit 28 will be described next.

Correction data 206 is input to the correction unit 52 from the inputunit 61. A barcode reader for reading and inputting a barcode or anoperation unit that is operated by the user to enter various data mayserve as the input unit 61. Alternatively, the correction data may beinput by installing an EEPROM in which the correction data has beenstored beforehand. Next, in sync with a BD signal 201 that is outputfrom beam detector 60, the current value or drive time of a drive(light-emission) signal 204 of the semiconductor laser 55 output fromthe laser driving controller 54 is controlled in accordance with theimage signal 202 generated by the image signal generator 53 and acorrection signal 203 that conforms to the optical characteristic of theoptical unit output from the correction unit 52. According to thecurrent control method of this embodiment, it is permissible to controlthe absolute value of the current or the time during which the currentis passed or both.

The laser beam 205 that has been emitted from the semiconductor laser 55is collimated by the collimating lens 56. The collimated laser beam isdeflected in the primary scan direction by the polygon mirror 57,thereby performing the primary scan. At this time optical distortionsuch as leaning of the plane is corrected by the fθ lens 58, the laserbeam is reflected by a mirror 59 and irradiates the surface of thephotosensitive drum 21 to form an electrostatic latent image on thesurface of the photosensitive drum 21. The electrostatic image thusformed on the photosensitive drum 21 is developed by the developer 13,and the developed image is transferred to and fixed on the printingsheet by a well-known electrophotography process.

FIG. 3 is a diagram useful in describing the correction performed by thecorrection unit 52 of the laser irradiation unit 28 according to thisembodiment.

Shown in FIG. 3 are an optical characteristic 70 of the unit 28 andcorrection resolution (number of items of data stored in memory) 71along the primary scan direction. In this embodiment, one scanning lineof pixels is divided into a plurality of blocks (nine blocks in theexample of FIG. 3) and a shading correction (73) is performed bychanging over the correction data in stages within each block.

Also shown in FIG. 3 are correction data 72 for optical properties, thisbeing data (old) for performing a shading correction, and correctiondata 73 for optical properties according to this embodiment, this databeing data (new) for performing a shading correction. At the timing atwhich the laser beam irradiates the photosensitive drum 21 based uponthe BD signal 201, the correction unit 52 outputs the correspondingoptical-properties correction data 73 to the laser driving controller 54as the correction signal 203, thereby controlling the driving of thesemiconductor laser 55. In the example of FIG. 3, the steps of thecorrection data 73 near both ends of one scanning line differ from thosenear the middle of the line. However, since the difference between itemsof correction data of adjacent correction intervals is small near themiddle of the line, step width is coarse as a result.

FIG. 4 is a block diagram illustrating the structure of the correctionunit 52 according to this embodiment.

The optical-property correction data 72 for the optical unit 28 isstored in a memory 74 in advance.

FIG. 5 is a diagram useful in describing the storage of the data in thememory 74.

A counter 75 is reset by the BD signal 201 and counts a pixel clock(CLK) 400 that is synchronized to the pixel data printed. The counter 75is, e.g., a 4-bit counter the output (OUT) 401 of which is a carrysignal produced whenever the counter 75 counts up to “16”. The value of“16” counted by the counter 75 corresponds to the number of pixels inone correction interval 71 of one scanning line indicated in FIG. 3.

The memory 74, which is a FIFO memory, for example, outputs correctiondata successively from a 0^(th) item of correction data, which is shownin FIG. 5, in sync (i.e., every 16 pixels) with the output 401 of thecounter 75.

A latch 76 latches the data, which has been output from the memory 74,in sync with the output of the counter 75. An arithmetic unit 77 obtainslinear interpolation data from two input signals comprising ADATA, whichis the output (W) of the latch 76, and BDATA, which is the output (X) ofthe memory 74. The OUT signal of the arithmetic unit 77 is output insync with the pixel clock (CLK) 400 and constitutes the correctionsignal 203, which is the optical-properties correction data 73 shown inFIG. 3.

FIG. 5 is a diagram useful in describing the placement of the correctiondata that has been stored in the memory 74.

The correction data 206 that has entered from the input unit 61 isstored in memory 74 from a 0^(th) address to an n^(th) address along theprimary scan direction.

The correction data is stored from address 0 of memory 74 in orderstarting from 0^(th) correction data of the primary scan direction.Whenever the CLK signal 400 enters, correction data is output from theaddresses in ascending order (i.e., from addresses 0 to n in the ordermentioned).

In this example, the correction data that has entered from the inputunit 61 is illustrated as being stored in the memory 74. However, in acase where an EPROM storing the correction data is provided, the EPROMmay serve as the memory and it may be so arranged that the correctiondata is read out of the memory (EPROM) directly.

FIG. 6 is a timing chart for describing the generation of correctiondata by the correction unit 52 of FIG. 4. Here one scanning line is 2048pixels, the scanning line is divided into 128 blocks (n=127) (correctionintervals (H1 to H128)) and each correction interval corresponds to 16pixels (m=16). Further, W represents the output of latch 76, X theoutput of memory 74 and b (203) the output of arithmetic unit 77.

The operation of the correction unit 52 will now be described withreference to FIGS. 4 to 6. The description will be rendered for a casewhere the correction interval of one scanning line corresponds to 16pixels, one scanning line is 2048 pixels and the number of correctionintervals per scanning line is 128 (n=127 in FIG. 5).

First, when the BD signal 201, which is output from the beam detector60, is input to the memory 74 and to a reset terminal (RST) of thecounter 75, the address of the memory 74 and the count value of thecounter 75 are cleared to “0”. The counter 75 is a 4-bit counter and theoutput (OUT) 401 thereof is a carry signal.

In correction interval H1, initially 16 pulses of the pixel clock signal(CLK) 400 enter as a dummy signal, whereupon the carry signal (OUT) 401of the counter 75 is output as a pulse signal of one clock. As a result,0^(th) correction data of the primary scan direction being output fromthe memory 74 is latched in the latch 76, and the output of the memory74 becomes the first item of correction data of the primary scandirection stored at the next address (see FIG. 5). As a result, the0^(th) correction data (W) of the primary scan direction enters theinput ADATA of the arithmetic unit 77, and the first item of correctiondata (X) of the primary scan direction enters the input BDATA of thearithmetic unit 77 from the memory 74. Accordingly, the arithmetic unit77 calculates the difference between the two inputs W and X, linearlyinterpolates the difference at “16” corresponding to the number ofpixels of one correction interval and outputs the interpolation data (73in FIG. 3) as correction signal b (203) in sync with the pixel clock(CLK) 400.

In other words, a linear interpolation is performed from two items ofcorrection data that have been stored at adjacent addresses of memory74, linearly interpolated correction data (1 to m in FIG. 6) finelydivided in units of 16 bits is calculated and this is output as newcorrection data (203).

Furthermore, the correction in the laser irradiation unit 28 isperformed by the laser driving controller 54 based upon the b signal203, thereby controlling the light-emission current value orlight-emission time of the semiconductor laser 55.

When correction interval H1 thus ends, the correction interval H2 startsnext, the pulse signal 401 is output from the counter 75, the first itemof correction data (W) of the primary scan direction that has beenoutput from the memory 74 is latched in the latch 76, and the output ofthe memory 74 becomes the second item of correction data (X) of theprimary scan direction stored at the next address. The arithmetic unit77 calculates the difference between the two inputs W and X, linearlyinterpolates the difference at “16” corresponding to the number ofpixels of one correction interval and outputs the interpolation data ascorrection signal 203 in sync with the pixel clock (CLK) 400. Thus,correction data in the correction interval H2 is generated and output asthe correction signal 203.

Thenceforth, and in similar fashion, the correction signal 203 is outputfrom the arithmetic unit 77 in every correction interval (H3 to H128),and drive of the semiconductor laser 55 is controlled based upon thecorrection signal 203.

In the first embodiment, an example in which the optical-propertiescorrection data for the laser irradiation unit 28 is stored in memory 74is described. However, it goes without saying that similar results willbe obtained even if density-unevenness correction data for thephotosensitive drum 21 is stored in the memory 74, the above-describedprocessing is executed and the laser driving controller 54 is controlledby the correction signal thus obtained.

In the example of FIG. 4, the memory 74 is described as being a FIFOmemory. However, the present invention is not limited to thisarrangement. For example, the memory 74 may be implemented by anordinary memory (RAM) and the count value from the counter 75 may beinput as the address of the memory 74. In this case, if the arrangementis applied to the above-described example, use is made of a first 4-bitcounter and a second counter for counting the carry output of the 4-bitcounter, and the output of the second counter is adopted as the addressof memory 74.

Alternatively, in the example described above, the address space ofmemory 74 is assumed to be 1028 addresses and each item of 0 to ncorrection data of the primary scan direction is stored at each address.However, by storing the 0^(th) item of correction data of the primaryscan direction at addresses 0 to 15 of memory 74, storing the first itemof correction data of the primary scan direction at addresses 16 to 31of memory 74, storing the second item of correction data of the primaryscan direction at addresses 32 to 47 of memory 74 and so on, anoperation similar to that of counter 75 and memory 74 in FIG. 4 can berealized using one counter that is counted up pixel by pixel, and amemory to which the output of this counter is input as the address.

Second Embodiment

A second embodiment of the present invention will now be described.

FIG. 7 is a block diagram for describing the correction unit 52 and thedriver circuit of the semiconductor laser 55 according to a secondembodiment of the present invention. Components similar to those in FIG.2 are designated by like reference characters.

In the first embodiment, the characteristic of the laser irradiationunit 28 or the characteristic of the photosensitive drum 21 iscorrected. The characterizing feature of the second embodiment, however,is that both corrections can be performed simultaneously in order toachieve even better image quality.

An optical correction data storage unit 79 stores the correction data ofthe laser irradiation unit 28. A sensitivity correction data storageunit 80 stores correction data for correcting sensitivity unevenness ofthe photosensitive drum 21. The sensitivity correction data storage unit80 corresponds to the memory 74 of the first embodiment. A linearinterpolator 82 performs linear interpolation of correction data thathas been read out of the optical correction data storage unit 79 orsensitivity correction data storage unit 80 and corresponds to thearithmetic unit 77 of the first embodiment. A calculation unit 83 addslinearly interpolated correction data from the linear interpolator 82.As a result, it is possible to correct the drive signal of thesemiconductor laser in accordance with the laser irradiation unit 28 andphotosensitive drum 21, thus making it possible to obtain a higher imagequality.

In the second embodiment, the correction data for the photosensitivedrum is stored in the sensitivity correction data storage unit 80.However, similar results can be obtained even by a method of measuringsurface potential of the photosensitive drum 21 in the primary scandirection using a surface electrometer, converting the measurement datato digital data and storing the digital data successively in thesensitivity correction data storage unit 80.

FIG. 8 is a flowchart for describing laser drive control in a colorprinter according to this embodiment of the present invention.

First, at step S1, one scanning interval of the laser beam is dividedinto a plurality of blocks and the number of pixels (16 in this example)corresponding to each block is obtained. Next, at step S2, the laserbeam is modulated in accordance with the image signal and laser scanningfor scanning the laser beam is started. This is followed by step S3, atwhich correction data corresponding to the block currently being scannedby the laser beam is read out of the memory 74. Then, at step S4correction data for the block neighboring this block is read out andcorrection data corresponding to the block currently being scanned bythe laser beam is decided (step S5) based also upon the data read out atstep S3 (by the interpolation described in the example above). Next, atstep S6, laser drive by the laser driving controller 54 is controlled inaccordance with the correction data obtained at step S5. Control by thelaser driving controller 54 is such that in addition to pulse-widthmodulation (PWM) conforming to the image signal, the pulse width of thispulse-width modulated signal, or the drive current that prevails whenthe pulse is applied, is adjusted in accordance with the correction dataof the kind shown in FIG. 3.

Next, at step S7, it is determined whether the block currently beingscanned has ended and the laser beam has shifted to the next block. Ifthe decision rendered is “NO”, then control returns to step S6. If thelaser beam has shifted to the next block (“YES” at step S7), then it isdetermined at step S8 whether one scan has ended. When one scan has notended, control returns to step S3 and the above-described processing isexecuted. In the case of the second embodiment, both correction data ofthe optical system and correction data of the photosensitive drum areread out at steps S3 and S4, and each type of correction data, namelythe correction data of the optical system and correction data of thephotosensitive drum, is decided at step S5.

The object of the invention is attained also by supplying a storagemedium storing the program codes of the software for performing thefunctions of the foregoing embodiment (e.g., the procedure of FIG. 8) toa system or an apparatus, reading the program codes with a computer(e.g., a CPU or MPU) of the system or apparatus from the storage medium,and then executing the program codes. In this case, the program codesread from the storage medium implement the novel functions of theembodiment and the storage medium storing the program codes constitutesthe invention. Examples of storage media that can be used for supplyingthe program code are a floppy disk, hard disk, optical disk,magneto-optical disk, CD-ROM, CD-R, magnetic tape, non-volatile typememory card or ROM, etc.

Furthermore, besides the case where the aforesaid functions according tothe embodiment are implemented by executing the program codes read by acomputer, it goes without saying that the present invention covers acase where an operating system or the like running on the computerperforms a part of or the entire process in accordance with thedesignation of program codes and implements the functions according tothe embodiment.

The present invention further covers a case where, after the programcodes read from the storage medium are written in a function expansionboard inserted into the computer or in a memory provided in a functionexpansion unit connected to the computer, a CPU or the like contained inthe function expansion board or function expansion unit performs a partof or the entire process in accordance with the designation of programcodes and implements the function of the above embodiment.

The present invention is not limited to the above embodiment, andvarious changes and modifications can be made thereto within the spiritand scope of the present invention. Therefore, to apprise the public ofthe scope of the present invention, the following claims are made.

CLAIM OF PRIORITY

This application claims priority from Japanese Patent Application No.2004-074711 filed Mar. 16, 2004, which is hereby incorporated byreference herein.

1. An image forming apparatus for irradiating an electrically chargedphotosensitive material with a laser beam and forming an electrostaticlatent image to thereby form an image, comprising: storage means fordividing one scanning interval of the laser beam into a plurality ofblocks, and storing correction data, which corresponds to opticalcharacteristics of an optical unit placed between a laser element andthe photosensitive material, in association with each block; readoutmeans for reading first correction data, which corresponds to a blockbeing scanned by the laser beam, out of said storage means; and drivingcontrol means for correcting a drive signal of the laser element anddriving the laser element based upon the first correction data, whichhas been read out by said readout means, and second correction data,which corresponds to a block adjacent the block being scanned by thelaser beam.
 2. An image forming apparatus for irradiating anelectrically charged photosensitive material with a laser beam andforming an electrostatic latent image to thereby form an image,comprising: storage means for storing correction data corresponding toelectrification characteristics of the photosensitive material; readoutmeans for reading first correction data, which corresponds to a blockbeing scanned by the laser beam, out of said storage means; and drivingcontrol means for correcting a drive signal of the laser element anddriving the laser element based upon the first correction data, whichhas been read out by said readout means, and second correction data,which corresponds to a block adjacent the block being scanned by thelaser beam.
 3. (canceled)
 4. The apparatus according to claim 1, whereinsaid driving control means obtains correction control data by performinglinear interpolation between the first correction data read out by saidreadout means and the second correction data corresponding to the blockadjacent the block being scanned by the laser beam, and correcting thedrive signal of the laser element and driving the laser element inaccordance with the correction control data.
 5. The apparatus accordingto claim 4, wherein said driving control means changes pulse width of alaser driving signal corresponding to pixel data, which is to form animage, in accordance with the correction control data.
 6. The apparatusaccording to claim 4, wherein said driving control means changes drivingcurrent of a laser driving signal corresponding to pixel data, which isto form an image, in accordance with the correction control data.
 7. Theapparatus according to claim 1, further comprising input means forinputting the correction data and storing it in said storage means. 8.The apparatus according to claim 2, wherein said driving control meansobtains correction control data by performing linear interpolationbetween the first correction data read out by said readout means and thesecond correction data corresponding to the block adjacent the blockbeing scanned by the laser beam, and correcting the drive signal of thelaser element and driving the laser element in accordance with thecorrection control data.
 9. The apparatus according to claim 8, whereinsaid driving control means changes pulse width of a laser driving signalcorresponding to pixel data, which is to form an image, in accordancewith the correction control data.
 10. The apparatus according to claim8, wherein said driving control means changes driving current of a laserdriving signal corresponding to pixel data, which is to form an image,in accordance with the correction control data.
 11. The apparatusaccording to claim 2, further comprising input means for inputting thecorrection data and storing it in said storage means.
 12. The apparatusaccording to claim 3, wherein said driving control means obtains firstand second correction control data by performing linear interpolationbetween the first and second correction data read out by said readoutmeans and respective ones of first and second correction datacorresponding to the block adjacent the block being scanned by the laserbeam, and correcting the drive signal of the laser element and drivingthe laser element in accordance with the first and second correctioncontrol data. 13.-14. (canceled)
 15. A method of controlling an imageforming apparatus for irradiating an electrically charged photosensitivematerial with a laser beam and forming an electrostatic latent image tothereby form an image, comprising: a step of dividing one scanninginterval of the laser beam into a plurality of blocks, and storingcorrection data, which corresponds to optical characteristics of anoptical unit placed between a laser element and the photosensitivematerial, in memory in association with each block; a readout step ofreading first correction data, which corresponds to a block beingscanned by the laser beam, out of said memory; and a driving controlstep of correcting a drive signal of the laser element and driving thelaser element based upon the first correction data, which has been readout in said readout step, and second correction data, which correspondsto a block adjacent the block being scanned by the laser beam.
 16. Amethod of controlling an image forming apparatus for irradiating anelectrically charged photosensitive material with a laser beam andforming an electrostatic latent image to thereby form an image,comprising: a step of storing correction data corresponding toelectrification characteristics of the photosensitive material; areadout step of reading first correction data, which corresponds to ablock being scanned by the laser beam, out of said memory; and a drivingcontrol step of correcting a drive signal of the laser element anddriving the laser element based upon the first correction data, whichhas been read out in said readout step, and second correction data,which corresponds to a block adjacent the block being scanned by thelaser beam.
 17. A method of controlling an image forming apparatus forirradiating an electrically charged photosensitive material with a laserbeam and forming an electrostatic latent image to thereby form an image,comprising: a step of dividing one scanning interval of the laser beaminto a plurality of blocks, storing first correction data, whichcorresponds to optical characteristics of an optical unit placed betweena laser element and the photosensitive material, in a first memory inassociation with each block, and storing second correction datacorresponding to electrification characteristics of the photosensitivematerial in a second memory; a readout step of reading the first andsecond correction data, which corresponds to a block being scanned bythe laser beam, out of said first and second memories; and a drivingcontrol step of correcting a drive signal of the laser element anddriving the laser element based upon the first and second correctiondata that has been read out in said readout step and first and secondcorrection data corresponding to a block adjacent the block beingscanned by the laser beam.
 18. The method according to claim 15, whereinin said driving control step, correction control data is obtained byperforming linear interpolation between the first correction data readout in said readout step and the second correction data corresponding tothe block adjacent the block being scanned by the laser beam, and thedrive signal of the laser element is corrected and the laser element isdriven in accordance with the correction control data.
 19. The methodaccording to claim 18, wherein in said driving control step, a pulsewidth of a laser driving signal is changed corresponding to pixel data,which is to form an image, in accordance with the correction controldata.
 20. The method according to claim 18, wherein in said drivingcontrol step, a driving current of a laser driving signal is changedcorresponding to pixel data, which is to form an image, in accordancewith the correction control data.
 21. The method according to claim 15,further comprising an input step of inputting the correction data andstoring it in the memory.
 22. The method according to claim 16, whereinin said driving control step, correction control data is obtained byperforming linear interpolation between the first correction data readout in said readout step and the second correction data corresponding tothe block adjacent the block being scanned by the laser beam, and thedrive signal of the laser element is corrected and the laser element isdriven in accordance with the correction control data.
 23. The methodaccording to claim 22, wherein in said driving control step, a pulsewidth of a laser driving signal is changed corresponding to pixel data,which is to form an image, in accordance with the correction controldata.
 24. The method according to claim 22, wherein in said drivingcontrol step, a driving current of a laser driving signal is changedcorresponding to pixel data, which is to form an image, in accordancewith the correction control data.
 25. The method according to claim 16,further comprising an input step of inputting the correction data andstoring it in the memory.